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The hackers who broke into iCloud accounts could have accessed revealing images and data users believed had been deleted weeks or even months in the past, an eagle-eyed Check Point Software researcher has discovered.

Check Point information security strategist Moti Sagey started looking into the issue after reading a Twitter post from actress Mary Winstead that has come to symbolize the bafflement celebrity victims have expressed in the face of an easy-to-use but also inscrutable technology.

Apple doesn't advertise it, but it turns out that iCloud for iOS saves the last three backup revisions for every device, which for anyone who opted into the service during setup (i.e. almost everyone) will happen once per day as long as Wi-Fi is activated and the device is plugged in and charging.

A few users will activate backups manually but many will just "set and forget" in which case the three backups inside iCloud will correspond to three consecutive days.

However, a smaller group, including those who travel a lot, might not have Wi-Fi activated while also charging as frequently, in which case the three backups inside the system could end up being days, weeks or even many months apart.

They won't know this of course because according to Sagey only the most recent backup appears. He discovered the two hidden backups while using a utility called DR.Fone that aids in iCloud backup recovery. While using the software he noticed that each iOS device had not one but three backups visible, holding files he believed to be long gone.

In simple terms, "if I look I will not see that I have these revisions," Sagey told Techworld. "I'm sure the hackers either knew this or just used a tool and discovered it by mistake," he said.

He speculates that having two hidden backups is probably a convenience for Apple in case the primary one corrupts during the transfer or simply as general insurance.

So Apple's design isn't a bad per se but might aid file trawlers when attacking a subset of users who don't back up often. It should already be clear to most users that simply deleting a file from an iOS device does not mean that it's gone from the iCloud too.